Cobalt phosphines

If cobalt carbonylpyridine catalyst systems are used, the formation of unbranched carboxylic acids is strongly favored not only by reaction of a-olefins but also by reaction of olefins with internal double bonds ( contrathermo-dynamic double-bond isomerization) [59]. The cobalt carbonylpyridine catalyst of the hydrocarboxylation reaction resembles the cobalt carbonyl-terf-phos-phine catalysts of the hydroformylation reaction. The reactivity of the cobalt-pyridine system in the hydrocarboxylation reaction is remarkable higher than the cobalt-phosphine system in the hydroformylation reaction, especially in the case of olefins with internal double bonds. This reaction had not found an industrial application until now. 

In contrast to rhodium and iridium, monoatomic cobalt has not been investigated extensively as a hydrosilylation catalyst, though one report discusses the use of cobalt phosphine complexes.54... 

It is interesting to note that no specific study was devoted to the aqueous biphasic hydrogenation of aldehydes with water-soluble cobalt-phosphine complexes, although such a property has long been known from hydroformylation experiments [199,200]. 

Mono- and double carbonylation of phenetyl bromide with cobalt-phosphine catalysts afforded benzylacetic (Baa) and benzylpymvic (Bpa) acids respectively [23] (Scheme 5.5). The highest yield of benzylpymvic acid (75 %) was obtained with [Co2(CO)8], while addition of the water soluble phosphines TPPMS or TPPTS decreased both the yield of carbonylated products and the selectivity to Bpa. 

Na5[Co+(CO)3(19)2]5 was used as catalyst for the hydroformylation of 1-hexene and 1-octene in a two phase system without leaching of cobalt into the organic phase.122 The products obtained were almost exclusively aldehydes (4-38%) and very little (0.4-3%) or no alcohol formation122 in contrast with cobalt/phosphine catalysed hydroformylation in organic solvents which give alcohols. The n/i ratios of the aldehydes were low (1.1-2.5),122 however, and never approached that expected for a phosphine modified cobalt catalyst in non-aqueous media324,325,393 (see Table 8). 

Cobaltocenium calix[4]arene receptors, characteristics, 12,475 Cobaltocenium-metallacarborane salts, preparation, 3, 23 Cobaltocenium receptors, characteristics, 12, 474 Cobalt phosphines, as supports, 12, 683 Cobalt-platinum nanoparticles, preparation, 12, 74 Cobalt-ruthenium clusters, as heterogeneous catalyst precursors, 12, 768... 

Process parameters Cobalt Cobalt + phosphine Rhodium + phosphine... 

In the first part of this article, focusing attention on polymer-supported cobalt phosphine complex 1 and arene ruthenium complex 2, we review contributions from our laboratory that show how organometallics can be efficiently attached to derivitised polystyrene and we outline their synthetic versatility.2,3 Following this, we discuss the preparation of a supported ruthenium complex, 3, and its use in oxidation and transfer hydrogenation catalysis. 

It has been shown that ligands such as phosphines can control the course of homologation reaction to a large extent. Tims, it seems likely that the Ugands are coordinated to the metal center during the catalytic cycle. Based on this assumption and on the observation that the best results were obtained with a cobalt-phosphine-iodide ratio of 1 2 2, Roper and Loevenich proposed the mechanism shown in Scheme 2. 

If the amounts of the catalyst ingredients (cobalt, phosphine, and base) are increased by the same factor without change in pressure and H2-to-CO ratio, the increase in phosphine concentration uncompensated by an increase in CO pressure shifts ligand exchange equilibrium toward HCo(CO)3Ph. Without base, this shift is at the expense of the more active HCo(CO)4, producing an apparent reaction order lower than one in "catalyst." In the presence of base, the shift is mostly at the expense of the inactive Co(CO)4, resulting in an apparent order higher than one. 

According to eqn 8.96, the reaction orders are plus one for total cobalt between zero and plus one for H2 and HB between zero and minus one for CO and B and between minus one and plus one for phosphine. Although the reaction is first order in cobalt, it may be of higher or lower order than first in "catalyst if the concentration ratios of the catalyst ingredients cobalt, phosphine, and base are held constant. This has been discussed in Example 8.3 in Section 8.2. 

Oshima and coworkers have developed a new epoxide ring-opening methodology treatment of a mixture of epoxide and styrene with trimethylsilylmethylmagnesium bromide in the presence of a cobalt-phosphine complex afforded the corresponding homocinnamyl alcohols in good yield (Scheme 35) <2004ASC1631>. 

Photocatalytic reductions may concern organic unsaturations (C=0, C=C, etc.), or inorganic CO2, or bicarbonate. Even carbon tetrachloride is very efficiently photo-reduced to chloroform by alcohols with mc.9o-tetra(2,6-dichlorophenyl)porphyrin [108]. Intermolecular hydrogen transfer is catalyzed by cobalt-phosphine complexes [109]. In this reaction photoirradiation generates the active hydride species CoH[PPh(OEt)2]3 for the reduction of ketones with secondary alcohols. The... 

Orsini, F., Pelizzoni, F., Pulici, M., Vallarino, L. M. A cobalt-phosphine complex as mediator in the formation of carbon-carbon bonds. J. 

Pettit, G. R., Grealish, M. P. A Cobalt-Phosphine Complex Directed Reformatskii Approach to a Stereospecific Synthesis of the Dolastatin 10 Unit Dolaproine (Dap). J. Org. Chem. 2001,66, 8640-8642. 

A method complementary to the palladium-catalyzed reaction has been reported. A cobalt-phosphine complex catalyzes a Heck-type reaction of alkyl halides with styrenes in the presence of Me3SiCH2MgCl [174]. Trimethylsilylmethylmag-nesium chloride was added to a mixture of styrene and bromocyclohexane in ether in the presence of a catalytic amount of CoCl2(dpph) at O C. Heating the reaction mixture under reflux (35°C) provided 163a in 91% yield (Scheme 3.158). 

Oxidations. Ketones are cleaved to afford carboxylic acids in moderate yields by ReiOv-t-BuOOH in acetic acid at 100°. Vanadium-catalyzed epoxidation of unsaturated alcohols in liquid carbon dioxide is feasible.- A resin-bound cobalt-phosphine complex is also effective as a catalyst for oxidation. ... 

The Shell process uses a cobalt/phosphine catalyst for the homologation of methanol CH3 - OH 4- CO + 2Hj - CH3CH2OH 4- H20... 

Figure 11 Proposed cobalt-phosphine hydroformylation and aldehyde hydrogenation cycles showing the dominant linear product selectivity.

Lim derivative was also studied using HP-NMR, and a mechanism for the formation of branched aldehyde products was proposed. Further work published by Crause et a described the effect of variation of the Lim alkyl chain. HP-NMR and HP-IR studies, combined with molecular modeling and autoclave experiments, showed that the primary factor governing performance of these ligands was the extent of phosphine-modified versus unmodified catalysis. Control of catalyst equilibria in favor of cobalt—phosphine species resulted in improved product linearities, but slower reaction rates. 

In addition to cobalt and Union Carbide s rhodium-phosphine catalysts for the hydroformylation process. Shell s cobalt/phosphine system has potential advantages, providing higher n-/iso-ratios than cobalt alone while producing mainly the alcohol in one step. 

Cobalt phosphine complexes of the type CpCo(diphosphine) have been known since 1986 to be molecular electrocatalysts for hydrogen production [80]. Catalysis by this family of compounds occurs through a [CpCo (diphosphine)H] intermediate that is only reduced at relatively large overpotentials. This limitation has led to... 

Metal Oxidation States in Nickel and Cobalt Phosphine Complexes... 

Cobalt-phosphine and cobalt-carbene catalysts have been developed for the hydroarylation of styrene with (91) via a chelation-assisted C-H bond activation. The regioselectivity can be controlled in favour of the branched (92) or linear product (93) at will by the ligand. Deuterium-labelling studies demonstrated a reversible C-H bond cleavage and alkene insertion steps and reductive elimination as the rate-and regioselectivity-determining step. ... 

In our first study, we reported on a method of clay intercalating cobalt phosphine complexes (e.g., CoCl2(PMePh2)2 and CoCl2(P PrPh2)2) which, in combina-... 

In many of these reactions the alkyne complex (A) which is first formed is converted into a metallacyclopentadiene (B), the key intermediate. This has been characterized in the cobalt phosphine system, which catalyses the cyclotrimerization of alkynes to arenes (e.g. 2-butyne to hexamethylbenzene) at 120°C (Fig. 7.13). 

The reaction of norbomadiene with an acetylene may follow different reaction channels, depending on the reaction conditions. Using a cobalt/phosphine catalyst, an acetylene adds to the two unsaturated front carbon atoms of norbomadiene, giving a five-membered cyclopentene ring. Simultaneously, a three-membered cyclopropane ling is formed at the backside of the molecule. The polycyclic skeleton obtained in this homo Diels-Alder reaction is called the deltacyclene skeleton (Scheme 4). 

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